The present invention relates to a device in which a load measuring mechanism of a weighing apparatus has a load of a weight incorporated in a weighing apparatus or the load measuring mechanism has no load of the weight by supporting the load of the weight, and particularly to a device that is suitably applied to the weighing apparatus collectively called an electronic scale.
Because the electronic scale such as an electromagnetic balancing type scale has high performance and high resolution, the electronic scale tends to heavily depend on an environment in which the electronic scale is placed as the weighing apparatus.
For example, a change in weighing value of the electronic scale is generated by a slight change in physical property, such as a latitude on a map of placement site, a temperature of a placement environment, a change in atmospheric pressure or attraction of the moon caused by movement of the moon, and a change in gravitational field caused by ground characteristics, which can substantially be ignored in the usual life environment. As to a gravitational acceleration distribution, it is known that the gravitational acceleration distribution has a difference of about 1/1000 in Japan.
Therefore, in high-end models such as high-performance electromagnetic balancing type weighing apparatus called an analytical balance having resolution exceeding 1/106 and models called a general-purpose balance having resolution of about 1/105, a weight for calibration is almost always incorporated therein, the calibration is performed by the weighing apparatus, and the proper measurement can always be made even if the change in physical property is generated in the placement environment.
FIG. 8 conceptually illustrates a method of performing the calibration using the built-in weight in the electromagnetic balancing type weighing apparatus. In the weighing apparatus, a weight W of a measured sample loaded on a pan 50 is transmitted to an electromagnetic portion 53 through a beam 52 guided by a Roverbal mechanism including upper and lower sub-beams 51a and 51b, an electric amount is supplied to the electromagnetic portion 53 so as to be balanced with an amount of displacement of the electromagnetic portion 53, and the weight W of the sample is measured based on the electric amount.
As described above, because the weighing value is possibly changed by the change of the placement environment in the electromagnetic balancing type weighing apparatus, periodically or appropriately by switch manipulation of a user, a built-in weight 54 with a precisely determined mass is loaded on a built-in weight load receiver portion 55 of a load measuring mechanism to perform the calibration of the weighing apparatus such that the weighing value of the built-in weight is matched with a mass of the built-in weight.
The weighing apparatus having the built-in weight has a mechanism that loads the built-in weight on the load measuring mechanism or pulls up the loaded built-in weight to bring the load measuring mechanism into a no-load state (hereinafter the operations are referred to as “addition and removal” of the built-in weight). Therefore, the appropriate calibration is automatically and periodically performed using a timer or by switch manipulation of the weighing apparatus user. Patent Documents listed below disclose a built-in weight addition and removal (lifting and lowering) mechanism that adds and removes the built-in weight in performing the calibration.
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-221682
Patent Document 2: Japanese Patent Application Laid-Open No. 11-160141
Patent Document 3: Japanese Patent Application Laid-Open No. 2000-097756
Patent Document 4: Japanese Patent Application Laid-Open No. 2000-121423
Patent Document 5: Japanese Utility Model Registration No. 2506662
Patent Document 6: U.S. Pat. No. 7,012,198
Patent Document 7: U.S. Pat. No. 5,148,881
Patent Document 8: U.S. Pat. No. 4,766,965